Variable resistor with rectangular resistance element



June 3, 1969 M. w. BANG ETJVAL VARIABLE RESISTOR WITH RECTANGULAR RESISTANCE ELEMENT Filed Oct. 25, 1967 f f 4( ETT T I" r Ii I A TTOR/VEKS J1me 1969 M. w. BANG ETAL 3,448,428

VARIABLE RESISTOR WITH RECTANGULAR RESISTANCE ELEMENT Sheet Q of 5 Filed 001. 23, 1967 147' 7' ORA/E V5.

June 3, 1969 M. w. BANG ETAL 3,448,428

VARIABLE RESISTOR WITH RECTANGULAR RESISTANCE ELEMENT Filed on. 25, 1967 147' 7' ORA E K9 United States Patent VARIABLE RESISTOR WITH RECTANGULAR RESISTANCE ELEMENT Mogens W. Bang and Earl A. Hanson, Ridgway, Pa., and Frederick E. Eichmiller, deceased, late of St. Marys, Pa., by Gloria Eichmiller, administratrix, St. Marys, Pa., assignors to Stackpole Carbon Company, St. Marys, Pa., a corporation of Pennsylvania Filed Oct. 23, 1967, Ser. No. 678,159 Int. Cl. H01c /02, 13/00 U.S. Cl. 338-162 13 Claims ABSTRACT OF THE DISCLOSURE Background of the invention Present rotary motion variable resistors have narrow circular resistance elements which utilize only a small part of the material [from which they are stamped, the rest being wasted. Masking is required in connection with the deposition of the resistance material, and the resistance element has a low wattage rating because of its limited surface area.

It is among the objects of this invention to provide a rotary motion 'variable resistor that has higher power capabilities, greater strength and a less expensive construction than heretofore.

The invention is illustrated in the accompanying drawings, in which FIG. 1 is a front view of our electrical resistance element, greatly enlarged;

FIG. 2 is a further enlarged lower edge viewthereof;

FIGS. 3 and 4 are similar views of a modification;

FIG. 5 is a front view of a further embodiment of the invention;

FIG. 6 is a cross section taken on the line VI--VI of FIG. 5;

FIG. 7 is a view of one side of a potentiometer incorporating the invention;

FIG. 8' is an edge view thereof;

FIG. 9 is a view of the opposite side;

'FIGS. 10, 11 and 12 are views similar to the three preceding figures of a further modification;

FIG. 13 is an enlarged cross section taken on the line X'HI-XI I'I of FIG.

FIGS. 14, 15 and 16 are views similar to FIGS. 10 to 12 of a still further modification; and

FIG. 17 is an enlarged cross section taken on the line XVII-XVI'I of FIG. 14.

Referring to FIGS. 1 and 2 of the drawings, a flat rectangular substrate is formed from a thin plate 1 of insulating material that preferably is square and has laterally spaced tongues 2 projecting from one or more edges. The two outside tongues are at adjacent corners of the substrate. This substrate supports an electrical resistance element 3 that is formed by applying a coating of resistance material to one side of the substrate. The coating extends to the edges of the substrate, and along the two corner tongues to form terminals 4. [If desired, however, the terminals may be formed from metal applied to the tongues and joined to the adjacent Patented June 3, 1969 edge of the resistance coating. The substrate and coating are provided with a central hole 5 therethrough for receiving a rotatable shaft (not shown).

In order to form a resistance path, there is a gap 6 in the resistance coating. The gap extends from the edge of the coating that is between the corner terminals toward the opposite edge of the element and then part way around the central hole. The outer end of this gap is close to one of the terminals 4. Preferably, the gap extends in a straight line about half way across the coating and then starts to curve around the central hole in an arc concentric with that hole. The portion of the resistance element between the gap and the nearest edges of the element forms the narrow part of the resistance path that will be engaged by a sliding contact. The distance that the gap extends around the hole therefore determines the length of this narrow or high resistance portion of the resistance path that is in series with the low resistance portion of the \path beyond the gap. One way of forming the gap is to form a groove 7 in the adjoining surface of the substrate before the resistance material is applied. During application of that material, care is taken that it does not extend down into the groove and bridge it. The resistance curve can be adjusted by punching holes 8 or a notch in either or both of the corners of the element and substrate opposite the terminals.

Another way of forming a gap 9 in such a resistance element 10, shown in (R168. 3 and 4, is either to cut a slot 11 in the substrate 12 before the resistance coating is applied, or to apply the resistance material first and then remove it where the gap is to be or cut both slot and gap simultaneously. This modificaton also illustrates a way in which the area of the low resistance portion of the element can be increased in order to lower the resistance of that portion. It is done by providing the substrate with one or more grooves 13 that are lined with the resistance material.

FIGS. 5 and 6 show a third way of producing a nonconducting area or gap 14. In this examples the substrate 15 is provided with an integral ridge 16 having the length and shape of the desired gap. The substrate then is coated with resistance material 17, which also covers the ridge. The next step is to remove the coating [from the top of the ridge in any suitable manner, such as by grinding, thereby leaving a gap in the coating as shown. If desired, the resistance curve can be straightened by providing the substrate with a second ridge 18 in the upper right hand corner concentric with bridge 16. The resistance material likewise is removed from this second ridge, so the material in the corner is inactive. This form of the invention also illustrates two other features that also could be shown in FIGS. 1 to 4. One of these features is a ridge 20 projecting from one \face of the substrate all around its edge and the edges of outer tongues 21. This ridge first is covered with the resistance material as it is applied to the substrate and then the material over the ridge is ground off to provide the resistance element with a definite, clean cut outer edge. The second feature is the holes or slots 22 through tongues 21. If these tongues are dipped in molten metal or plated with metal to form terminals 23, the sides of the slots likewise would be coated to form electrical connection between the opposite sides of the tongues in spite of the metal around the edges being ground off ridge 20.

Any of the elements just described can be formed into a variable resistor or potentiometer in the manner disclosed in FIGS. 7 to 9, but the element shown in FIGS. 1 and 2 will be used as an example. Thus, a metal current collector 24 is applied to the reverse side of the substrate 1 in any suitable manner. The collector may take the form of a square plate or a ring concentric with the central hole through the substrate. A radial projection from the collector extends along the central tongue of the substrate to form a terminal 25. A rotatable shaft 26 is journaled in the central hole and supports at each side of the substrate a spring contact finger 27 having a contact 28 at its outer end. One of these contacts slidingly engages the collector ring, and the other contact engages the resistance coating 3 in such a location that the arcuate path 29 in which the contact moves extends between the curved portion of the resistance gap 6 and the adjacent edge of the resistance element. The farther the inner end of the gap extends around the shaft, the longer is the narrow portion of the resistance path between the gap and the closest outside edge of the resistance element, and consequently the longer the high resistance portion of the total resistance path.

Another application of this invention is illustrated in FIGS. to 13. In this case a substrate 30 with its resistance coating 31 is used as one side of an insulated housing 32. The substrate and housing are held together by a metal clip 33 provided with a central opening that may receive a bushing 34 mounted in a larger opening 35 in the adjacent side wall of the housing in line with the hole 36 through the substrate. The clip can be bent into place or it can be a spring clip. A rotatable shaft 37 extending through the substrate is journaled in the bushing. Engaging the inner surface of the housing opposite the resistance element is a square metal current collector plate 38 provided at one edge with a terminal 39 extending out of the housing. Between this collector and the resistance element there is an insulating rotor 41 that is rigidly mounted on the flattened portion of the shaft. Near one edge of the rotor it is provided with an opening 42 through it that receives a metal bridging contact 43, which frictionally engages both the collector and the resistance element. Preferably, this contact is cylindrical in the form of a wide ring or a coil spring. When the shaft is turned, it will cause the bridging contact to slide along the collector and also along the resistance element between its gap 44 and the adjacent edge of the element. Taps 45 for the resistance element may be formed by providing the substrate with additional tongues coated with the resistance material, like tongues 46.

The resistance element shown in this last described potentiometer illustrates a way in which elements of the same construction can be provided with narrow resistance paths of different lengths as desired. This is done by providing all of the substrates with ridges 47 that extend the same distance around the center holes, such as about threequarters of the way around them, and then removing the resistance coating from the top of all of each ridge or only for a predetermined distance from the outer end of the ridge. The longer the length of the portion of the ridge from which the resistance material is removed, the smaller the percentage of the total resistance formed by the low resistance part of the element.

In the embodiment of the invention shown in FIGS. 14 to 17, a box-like housing 50 has a cover 51 for its open bottom. Inside the housing, a rectangular metal collector plate 52 is disposed against one side. It is provided with a terminal 53 extending out through a slot in the cover. Opposite the plate is a rectangular insulating substrate 55 provided with two tongues 56 and 57 projecting through slots in the cover. In the upper corners of the housing it has integral spacing webs 58 spaced from the opposite sides of the inside of the housing just far enough to receive snugly the upper corners of the collector plate and the substrate 55 to hold those elements against the housing. The exposed surface of the substrate is covered with a film 59 of resistance material, except at the top of a ridge 60 that curves part way around the center of the substrate to form an arcuate resistance path.

The oppsite sides of the housing and the collector and substrate are provided centrally with aligned openings,

in which a control shaft 62 is rotatably mounted. The portion of the shaft extending through the housing and for a short distance beyond it is flattened. At the inner end of the flattened portion a collar 63 fits around it and is provided with a radial lug 64, the sides of which can engage a stop 65 projecting from the side of the housing to limit rotation of the shaft in opposite directions. The shaft can be held in place by a split ring 66 snapped into grooves in the projecting flattened end of the shaft.

Mounted on the control shaft between the collector and resistance film is a rotor 67 that fits the shaft and therefore must rotate with it. Near its periphery, the rotor is provided with an opening 68 therethrough, in which a metal bridging contact 69 is disposed. This contact may take the form of a ring, for example. It projects from the opposite side of the rotor into engagement with the collector and the resistance element. The rotor can be kept from rubbing on ridge 61 by spacing it away from the ridge by tiny bosses 70 projecting from the substrate. To avoid loose play between the rotor and its shaft, the rotor is provided with slots 71 therethrough parallel .to the flat sides of the shaft on opposite sides thereof. These slots are close enough to the shaft that the intervening portions of the rotor form slightly resilient strips 72, which grip the shaft between them to hold the rotor on the shaft firmly.

Any of the resistance elements described herein have resistance coatings with surface areas much larger than in the case of conventional narrow circular resistance films in variable resistors or potentiometers of the same dimensions. Consequently, the new elements should be able to dissipate a correspondingly greater amount of heat, thereby permitting a much greater wattage rating than before.

According to the provisions of the patent statutes, we have explained the principle of our invention and have illustrated and described what we now consider to represent its best embodiment.

We claim:

1. An electrical resistance element for a rotary motion variable resistor, comprising a substrate, a coating of resistance material thereon in substantially rectangular shape, a pair of laterally spaced electric terminals projecting from an edge of the coating, at least one of the terminals being at a corner of the coating, said coating having a gap therein extending from said edge between said terminals toward its opposite edge and then part way around the center of the coating, and the outer end of said gap being adjacent said one terminal.

2. An electrical resistance element as recited in claim 1, in which said substrate is substantially square.

3. An electrical resistance element as recited in claim 1, in which said substrate is provided with lateral projections supporting said terminals, and the terminals are integral with said coating.

4. An electrical resistance element as recited in claim 1, in which said substrate is provided with at least one groove to increase its surface area, and said groove is coated with said resistance material.

'5. An electrical resistance element as recited in claim 1, in which said gap is a slit in said resistance coating.

6. An electrical resistance element as recited in claim 1, in which said gap is formed from a ridge projecting from the surface of said substrate, with the resistance coating removed from the top of the ridge for at least part of the distance from the outer end of the ridge to its inner end.

7. An electrical resistance element as recited in claim 1, in which said substrate is rectangular and provided with an integral exposed ridge bordering said resistance coating.

8. An electrical resistance element as recited in claim 1, in which said substrate and coating are provided with a hole therethrough at the center of the substrate, and said element includes a current collector disposed on the opposite side of said substrate around said hole, and an electric terminal connected with said collector.

9. A potentiometer comprising a substrate, a coating of resistance material thereon in substantially rectangular shape, the substrate and coating having a hole therethrough for a rotatable control shaft, a pair of electric terminals projecting from an edge of the coating, at least one of the terminals being at a corner of the coating, said coating having a gap therein extending from said edge between said terminals toward its opposite edge and then partway around said hole, the outer end of said gap being adjacent said one terminal, a current collector disposed on the opposite side of the substrate around said hole, an electric terminal connected with said collector, a control shaft rotatably mounted in said hole and projecting from both sides of the substrate, a contact secured to the shaft and slidingly engaging said collector, and a second contact secured to the shaft and slidingly engaging said resistance coating in a position to be moved in an arcuate path extending between the outside of said gap and the edge of the coating.

10. A potentiometer comprising a substrate, a coating of resistance material thereon in substantially rectangular shape, a pair of electric terminals projecting from an edge of the coa-ting, at least one of the terminals being at a corner of the coating, said coating having a gap therein extending from said edge between said terminals toward its opposite edges and then part way around the center of the coating, the outer end of the gap being adjacent said one terminal, arcurrent collector facing said resistance coating and spaced therefrom, an electric terminal connected with said collector, a metal bridging contact between said coating and collector and engaging both, and means for moving said contact in an arcuate path extending between the outside of said gap and the edge of the coating.

11. A potentiometer according to claim, 10, in which said contact-moving means is a rotatable shaft extending through the centers of said collector and coating and substrate, and a housing encloses said coating and collector and supports the shaft.

12. A potentiometer according to claim 10, including a housing containing said collector and substrate, and a rotor disposed between the collector and substrate and provided with an opening containing said bridging contact, said contact-moving means being a shaft rotatably mounted in the opposite sides of the housing and rigidly supporting said rotor for turning it.

13. A potentiometer according to claim 10, including a housing containing said collector and substrate, and a rotor disposed between the collector and substrate and provided with an opening containing said bridging contact, said contact-moving means being a shaft rotatably mounted in the opposite sides of the housing and provided with a flattened portion extending through the rotor, and the rotor being provided near each side of the shaft with a slot substantially parallel to said flattened portion to form a resilient strip integral with the rotor pressing against the shaft.

References Cited UNITED STATES PATENTS 3,397,374 8/1968 Bang 338-162 1,767,715 6/ 1930 Stoekle 338-311 X 2,962,393 11/ 1960 Ruckelhaus -L. 117-212 2,744,987 5/1956 Marvin 338-311 X 2,886,854 5/1959 Franklin t 338-311 X 2,837,619 6/1958 Stein 338-308 X FOREIGN PATENTS 886,488 1/196-2 Great Britain. 839,315 6/1960 Great Britain.

LEWIS H. MYERS, Primary Examiner. A. T. GRIMLEY, Assistant Examiner.

, US. 01. X.R. 338-174, 183, 185, 30s 

